Computer systems generally utilize auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive read sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR element”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which an MR element resistance varies as the square of the cosine of the angle between the magnetization of the MR element and the direction of sense current flowing through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage.
Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers.
GMR sensors using only two layers of ferromagnetic material separated by a layer of non-magnetic electrically conductive material are generally referred to as spin valve (SV) sensors manifesting the GMR effect (SV effect). In a spin valve sensor, one of the ferromagnetic layers, referred to as the pinned layer, has its magnetization typically pinned by exchange coupling with an antiferromagnetic (e.g., NiO, Fe-Mn, PtMn) layer. The magnetization of the other ferromagnetic layer, referred to as the free layer, however, is not fixed and is free to rotate in response to the field from the recorded magnetic medium (the signal field). In spin valve sensors, the spin valve effect varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the free layer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium causes a change in the direction of magnetization in the free layer, which in turn causes a change in resistance of the spin valve sensor and a corresponding change in the sensed current or voltage. It should be noted that the AMR effect is also present in the spin valve sensor free layer and it tends to reduce the overall GMR effect.
FIG. 1 shows a typical sensor 100 (not drawn to scale) comprising end regions 104 and 106 separated by a central region 102. The central region 102 has defined edges and the end regions are contiguous with and abut the edges of the central region. As shown, a free layer (free ferromagnetic layer) 110 is positioned above a pinned layer (pinned ferromagnetic layer) 120. In the case of the GMR sensor, the free layer 110 and pinned layer 120 may be separated by a non-magnetic, electrically-conducting spacer 121.
The magnetization of the pinned layer 120 is fixed through exchange coupling with an antiferromagnetic (AFM) layer 125. Free layer 110, pinned layer 120 and the AFM layer 125 are all formed primarily in the central region 102. Hard bias layers 130 and 135 formed in the end regions 104 and 106, respectively, provide longitudinal bias for the free layer 110. Leads 140 and 145 formed over hard bias layers 130 and 135, respectively, provide electrical connections for the flow of the sensing current IS from a current source 160 to the MR sensor 100. Sensor 170 is connected to leads 140 and 145 senses the change in the resistance due to changes induced in the free layer 110 by the external magnetic field (e.g., field generated by a data bit stored on a disk). IBM's U.S. Pat. No. 5,206,590 granted to Dieny et al. and incorporated herein by reference, discloses an MR sensor operating on the basis of the spin valve effect.
In an MR sensor 100 such as that of FIG. 1, the magnetization of the free layer 110 is perpendicular to the magnetization of the pinned layer 120. FIG. 2 illustrates the manner in which the magnetizations of the free layer 110 and the pinned layer 120 are perpendicular, in accordance with the prior art. In use, this relationship must be maintained between the leads 140 and 145 (i.e. in an active region) to ensure proper operation and the proper “MR-pick up effect.”
Unfortunately, portions of the free layer 110 and the pinned layer 120 beneath the leads 140 and 145 (i.e. in an inactive region) sometime exhibit the foregoing relationship, which results in an undesireable MR-pick up effect. In particular, the free layer 110 and the pinned layer 120 beneath the leads 140 and 145 may “pick up” interference or other unwanted signals, thus reducing the reliability of the MR sensor 100. This also makes it difficult to define a track width because the end regions read a read signal during use. It should be noted that there is a continuing desire to make the trackwidth smaller so that more tracks can be fit onto a disk.
There is thus a need for a MR sensor that reads signals only in an active region between a pair of leads, without exhibiting a side MR-pick up effect.